This is a randomized trial of two standard approaches to therapy of patients with multiple sclerosis remaining active despite therapy with beta-interferons. One arm receives cytoxan plus solumedrol plus continued beta-interferons, while the other receives only solumedrol plus beta-interferons. There will be 20 patients at BWH and 20 at MGH, stratified for disease severity assessed by number of gadolinium lesions. This is an investigator-initiated, industry sponsored clinical trial.